Password changes are required for mods and admins as a security measure and it also helps when one of the staff decides to stop visiting. If someone suddenly shows up after 6 months/a year or more, there is a chance that it may not be who we think they are. Plus it also helps when a computer changes hands (sold, stolen, etc). There are a number of things that could happen.
I have so many passwords for banking, e-mails, websites, work stiff, etc that I have a hard time keeping track of it all. I use a program called Password Safe at work, and I used to use Whisper at home, but now I just use the keychain on the MAC. Password Management software is a good thing.